Rask turned aside 41 shots and Brad Marchand netted a pair of goals as the Bruins won their second straight after a two-game losing streak.
Stevens couldn't immediately halt the Kings' slide, in which they've lost five straight and have yet to score more than two goals in a game over nine contests.
Jonathan Quick was saddled with the loss, yielding all three goals on 22 shots in the setback.
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